288 KELVIN 



zontally, through a great distance. Thus the primary 

 phenomenon of the tides is after all the tidal current; and 

 it is the tidal currents that are referred to on charts 

 where we have arrow-heads marked with the statement 

 that we have "very little tide here," or that we have "strong 

 tides" there. 



One instance of great interest is near Portland. We hear 

 of the "race of Portland" which is produced by an exceed- 

 ingly strong tidal current; but in Portland harbour there is 

 exceedingly little rise and fall, and that little is much con- 

 fused, as if the water did not know which way it was go- 

 ing to move. Sometimes the water rises, sinks, seems to 

 think a little while about it, and then rises again. The 

 rise of the tide at Portland is interesting to the inhabitants 

 of Souhampton in this, that whereas here, at Southampton, 

 there is a double high water, there, at Portland, there is a 

 double low water. The double high water seems to extend 

 across the Channel. At Havre, and on the bar off the en- 

 trance to Havre, there is a double high water very useful 

 to navigation; but Southampton I believe is pre-eminent 

 above all the ports in the British Islands with respect to 

 this convenience. There is here (at Southampton) a good 

 three hours of high water; a little dip after the first high 

 water, and then the water rises again a very little more 

 for an hour and a half or two hours, before it begins to 

 fall to low water. 



I shall endeavour to refer to this subject again. It is not 

 merely the Isle of Wight that gives rise to the phenom- 

 enon. The influence extends to the east as far as Christ- 

 church, and is reversed at Portland, and we have the double 

 or the prolonged high water also over at Havre; therefore, 

 it is clearly not, as it has been supposed to be, due to the 

 Isle of Wight. 



But now I must come back to the question, What are the 

 "Tides"? Is a "tidal wave" a tide? What is called in the 

 newspapers a "tidal wave" rises sometimes in a few min- 

 utes, does great destruction, and goes down again, some- 

 what less rapidly. There are frequent instances in all parts 

 of the world of the occurrence of that phenomenon. Such 

 motions of the water, however, are not tides; they are 



